The present invention relates generally to the growth of films on substrates and methods of growing films on substrates using catalysts at or near room temperatures. More specifically, the present invention relates to the methods of growing film on substrates at room temperatures using catalyzed binary reaction sequence chemistry.
The development of low temperature ultra thin film deposition techniques will facilitate the development of many new technologies. Specifically, future silicon microelectronic devices will require multilevel fabrication techniques with components having nanoscale sizes in order to achieve ultra large scale integration. The reduction of component size and tolerances to the nanometer level will require extremely precise control over thin film properties such as film thickness, morphology, crystallinity, conformality and electrical properties.
However, currently available film deposition techniques require elevated temperatures ranging from 200.degree. C. to 1000.degree. C. Lower deposition temperatures will be needed because the interlayer diffusion of just a few atoms caused by high temperature can destroy the electrical and optical properties of such nanoscale devices.
Further, it is anticipated that silicon dioxide and ultra thin silicon dioxide films will be used in the nanoscale devices of the future because silicon dioxide has the best interface with silicon. Currently, silicon dioxide is used for many applications including optical fiber communication, microelectronics, protective coatings, electroluminescent displays, chromatography and others.
In order to push dynamic random access memory (DRAM) into the one gigabyte range, ultra thin silicon dioxide film deposition will need to be controlled on the atomic level. Further, very large flat panel displays will require extremely precise silicon dioxide film deposition on extremely large substrate areas. It is also anticipated that ultra thin silicon dioxide films will be used in multiple layer structures in order to tailor the mechanical, electrical and optical properties of technologically important materials.
Accordingly, there is a need for the development of low temperature ultra thin silicon dioxide film deposition. Currently, the ultra thin deposition of silicon dioxide may be achieved using an atomic layer controlled growth of a silicon dioxide film that incorporates a binary reaction sequence. Each half-reaction occurs on the growing surface and involves a reaction between a gas phase precursor and a surface functional group.
In the case of silicon dioxide thin film formation, the first functional group (OH) is bonded to the initial silicon or silicon dioxide surface to provide a functionalized substrate surface (Si--OH*). A first molecular precursor (SiCl.sub.4) bonds to the first functional group (OH*) and links a primary element atom (Si) between the first functional group (OH*) and a second functional group (Cl*) as shown in half-reaction A below. Then, in half-reaction B, the second functional group (Cl*) is displaced by a "new" first functional group (OH*) that is provided by a second molecular precursor (H.sub.2 O) as shown in half-reaction B below: EQU Si--OH*+SiCl.sub.4 .fwdarw.SiO--Si--Cl.sub.3 *+HCl (A) EQU Si--Cl*+H.sub.2 O.fwdarw.Si--OH*+HCl (B)
In half-reaction A, the Si--OH* represents a functionalized substrate surface or an otherwise functionalized silicon atom. The silicon tetrachloride reacts with the OH group resulting in a bond between the oxygen atom of the OH group and the silicon atom of the silicon tetrachloride with hydrochloric acid as a byproduct. Then, a second molecular precursor group in the form of water as shown in half-reaction B or hydrogen peroxide is provided which attacks one of the Si--Cl bonds to create a new functionalized silicon atom or Si--OH* bond. Successive application of the half reactions A and B produce a layer-by-layer silicon dioxide deposition. The resulting silicon dioxide films are highly uniform and extremely smooth. Each reagent is removed from the deposition chamber between successive reactions by means of evacuation or inert gas purging.
However, the drawback to the above technique is that it requires temperatures of greater than 600.degree. K and reactant exposures of greater than 10.sup.9 L for the surface reactions to reach completion (1 L=10.sup.-6 Torr sec). As noted above, high temperature procedures will not be acceptable for ultra-thin film deposition because of the likelihood of interlayer diffusion.
As a result, there is a need for an improved atomic layer controlled growth of thin films that can be carried out at low temperatures and requires much smaller fluxes of reagents.